import { InternalServerErrorException } from '@nestjs/common';
import { createCipheriv, createDecipheriv, randomBytes } from 'crypto';
import { envs } from 'src/config';

const ALGORITHM = 'aes-256-cbc';
const IV_LENGTH = 16;

function getKey(): Buffer {
  const raw = envs.aiEncryptionKey ?? '';
  if (raw.length !== 32) {
    throw new InternalServerErrorException('AI_ENCRYPTION_KEY debe tener exactamente 32 caracteres');
  }
  return Buffer.from(raw, 'utf8');
}

export function encryptKey(text: string): string {
  const iv = randomBytes(IV_LENGTH);
  const cipher = createCipheriv(ALGORITHM, getKey(), iv);
  const enc = Buffer.concat([cipher.update(text, 'utf8'), cipher.final()]);
  return `${iv.toString('hex')}:${enc.toString('hex')}`;
}

export function decryptKey(encrypted: string): string {
  const [ivHex, dataHex] = encrypted.split(':');
  const iv = Buffer.from(ivHex, 'hex');
  const data = Buffer.from(dataHex, 'hex');
  const decipher = createDecipheriv(ALGORITHM, getKey(), iv);
  const dec = Buffer.concat([decipher.update(data), decipher.final()]);
  return dec.toString('utf8');
}